Open the Recruit panel by pressing the Recruit button above the panel area on the right side of the game screen.

The Recruit panel can be used to invite up to five other people at once to join your nation. Simply enter your own name or nickname, and up to five e-mail addresses. Then press the "Submit" button. E-mails will be sent to each of the people whose addresses you entered, inviting them to join your nation and providing your nation's name and password.

The Recruit panel.